The broad field of applied chemistry involves (among other things) manufacture of chemical compounds and use of such compounds in other manufacturing activity or in treatment of articles of manufacture. Such chemical compounds may include toxic and hazardous substances, petrochemical products and the like. And such compounds may be volatile.
During manufacture and use of such compounds, it is often required that some aspect of the compound be tested or analyzed periodically. Such testing or analysis may be to help maintain compound purity, to determine its concentration in a dilute mixture or merely to determine whether such compound is present in or absent from a particular process.
Earlier practice in this field involved providing a simple drain or sampling faucet in the wall of a vessel or in a flow line containing the compound. A sample was drawn into an open container and any residual compound which dripped from the faucet was permitted to fall to the earth or to the room floor.
Increasing concerns about maintaining the environmental quality of the earth and the air have largely eliminated such practices, at least where anything but an innocuous compound is involved. Such concerns have been evidenced by the proliferation of legislation directed to, among other things, sampling practices.
For example, in the United States, the 1990 amendments to the Clean Air Act of 1970 expanded the list of volatile organic compounds (VOCs) and hazardous air pollutants from seven to over one hundred eighty products. Such amendments also established leak standards for fugitive emissions for pumps, valve, compressors sampling connection systems and other devices and systems. As a result, the techniques for taking samples of, e.g., volatile organic compounds (VOCs) and the equipment used for doing so have been dramatically revised.
The following describes some aspects of known sampling-type devices. Among the features of such known devices are partial path purging, bevelled hypodermic-like needles apt to core the septum, single valve shutoff and the like. The patents mentioned below describe further specifics.
The machine-like injector shown in U.S. Pat. No. 5,012,845 (Averette) uses a needle having dual concentric passages. After injection is complete, the needle is drawn upward into a valve block until its lower side port is in registry with a source of purging gas. Needle purging is "upstream," i.e., the purging gas and any liquid advanced by it is forced into the transparent barrel. The outer annular passage is apparently not purged at all.
The device shown in U.S. Pat. No. 4,580,452 (Masson) has a type of ball valve and a truncated valving stem seated in a cone-shaped aperture in the side wall of a liquid process line. Other hardware, with or without an additional shutoff valve, is connected to the side wall when a sample is to be drawn. The advantages are said to be that the device has no "dead volume" and a sample can be drawn without leakage to the environment. The patent describes purging before taking a sample and observes that the invention eliminates the need for such purging.
U.S. Pat. No. 4,823,623 (Carpenter et al.) describes a transfer device having a two-way valve, a pair of needles of different lengths and spaced guide rods which guide a vial into position. Trade literature of Tech-Quip, Inc. (a/k/a Texas Sampling Inc.) depicts a liquid sampler having a single two-way ball valve rotatable to "through-flow" or sampling positions but not both simultaneously. The sampling needles are hypodermic-like and the protective bottle shroud has an internal sleeve and an axial sight groove. Trade literature of Dopak Inc. illustrates other types of sampling devices.
Needles shown in the Carpenter et al. patent and Tech-Quip, Inc. literature are sharply pointed, bevelled and have downward-opening passages. Such needles are precisely the shape most likely to "core" the receptacle septum as it is being pierced by the needles.
And some of the prior art devices are understood to retain a significant "dead volume" of liquid after the liquid sample is taken. Such dead volume can drip and contaminate the surroundings or undesirably evaporate into the atmosphere.
An improved sampling valve assembly which offers redundant shutoff, low pressure sampling, optional "full-passage" purging, substantial avoidance of septum coring and minimum "dead volume" would be an important advance in the art.